Conventional devices for visualizing interior regions of a body lumen are known. For example, ultrasound devices have been used to produce images from within a body in vivo. Ultrasound has been used both with and without contrast agents, which typically enhance ultrasound-derived images.
Other conventional methods have utilized catheters or probes having position sensors deployed within the body lumen, such as the interior of a cardiac chamber. These types of positional sensors are typically used to determine the movement of a cardiac tissue surface or the electrical activity within the cardiac tissue. When a sufficient number of points have been sampled by the sensors, a “map” of the cardiac tissue may be generated.
Another conventional device utilizes an inflatable balloon which is typically introduced intravascularly in a deflated state and then inflated against the tissue region to be examined. Imaging is typically accomplished by an optical fiber or other apparatus such as electronic chips for viewing the tissue through the membrane(s) of the inflated balloon. Moreover, the balloon must generally be inflated for imaging. Other conventional balloons utilize a cavity or depression formed at a distal end of the inflated balloon. This cavity or depression is pressed against the tissue to be examined and is flushed with a clear fluid to provide a clear pathway through the blood.
However, such imaging balloons have many inherent disadvantages. For instance, such balloons generally require that the balloon be inflated to a relatively large size which may undesirably displace surrounding tissue and interfere with fine positioning of the imaging system against the tissue. Moreover, the working area created by such inflatable balloons are generally cramped and limited in size. Furthermore, inflated balloons may be susceptible to pressure changes in the surrounding fluid. For example, if the environment surrounding the inflated balloon undergoes pressure changes, e.g., during systolic and diastolic pressure cycles in a beating heart, the constant pressure change may affect the inflated balloon volume and its positioning to produce unsteady or undesirable conditions for optimal tissue imaging. Additionally, imaging balloons are subject to producing poor or blurred tissue images if the balloon is not firmly pressed against the tissue surface because of intervening blood between the balloon and tissue.
Accordingly, these types of imaging modalities are generally unable to provide desirable images useful for sufficient diagnosis and therapy of the endoluminal structure, due in part to factors such as dynamic forces generated by the natural movement of the heart. Moreover, anatomic structures within the body can occlude or obstruct the image acquisition process. Also, the presence and movement of opaque bodily fluids such as blood generally make in vivo imaging of tissue regions within the heart difficult.
Other external imaging modalities are also conventionally utilized. For example, computed tomography (CT) and magnetic resonance imaging (MRI) are typical modalities which are widely used to obtain images of body lumens such as the interior chambers of the heart. However, such imaging modalities fail to provide real-time imaging for intra-operative therapeutic procedures. Fluoroscopic imaging, for instance, is widely used to identify anatomic landmarks within the heart and other regions of the body. However, fluoroscopy fails to provide an accurate image of the tissue quality or surface and also fails to provide for instrumentation for performing tissue manipulation or other therapeutic procedures upon the visualized tissue regions. In addition, fluoroscopy provides a shadow of the intervening tissue onto a plate or sensor when it may be desirable to view the intraluminal surface of the tissue to diagnose pathologies or to perform some form of therapy on it.
In one particular treatment, intravascular stents are commonly used to maintain the patency of a vascular lumen. Conventional stent delivery systems typically employ intravascular ultrasound (IVUS) for selecting the appropriate stent and placing it at the site of lesions, e.g., ostial lesions. However, such assessment and placement methods are not accurate. For instance, the treatment site may be located in the right coronary artery immediately adjacent to the ostium in the aortic wall. In such instances, it is often difficult to accurately position an intravascular stem such that the stent does not extend too far proximal to the ostium. Accuracy in placing the stent at the desired location is typically affected by, e.g., limited visualization of the ostium, angulations of the aorto-coronary segment, and the difficulties in the placement of the guiding catheter.
Accurate positioning of the stent along the ostial lesion is particularly desirable because (a) if the stent is placed too proximal to the ostium, the protrusion of the stent into the aortic lumen can cause thrombus or other complications; and (b) if the stent is placed too distal to the ostium, the stent may not be able to subdue the ostial lesion completely thereby resulting in low success rate and high incidence of re-stenosis or recurrence of arterial blockage.
Thus, methods and/or apparatus which are able to allow for accurate positioning of the stent relative to the ostial lesion is highly desirable.